Temperature dependence of relative permittivity: role of permanent dipoles Assertion (A): In some materials, the relative permittivity εr is essentially independent of temperature, while in others εr varies with temperature. Reason (R): If permanent dipoles are absent, εr varies with temperature.

Introduction / Context:Dielectric behavior depends on the available polarization mechanisms: electronic, ionic, and orientational (dipolar). Understanding which mechanisms are present explains why the relative permittivity εr may be temperature-independent in some materials and strongly temperature-dependent in others.

Given Data / Assumptions:

• Nonpolar (no permanent dipoles) solids exhibit primarily electronic (and sometimes ionic) polarization.
• Polar materials possess permanent dipoles that can orient in an applied field.
• Thermal agitation affects orientational polarization significantly.

Concept / Approach:Electronic and ionic polarizations respond very rapidly and show weak temperature dependence over moderate ranges. In contrast, orientational polarization from permanent dipoles follows a Curie-like behavior, roughly proportional to 1/T, making εr decrease as temperature rises. Hence, εr can be nearly temperature-independent when permanent dipoles are absent, and temperature-dependent when they are present.

Step-by-Step Solution:Accept Assertion: Some materials show temperature-independent εr (nonpolar), others show temperature-dependent εr (polar) → True.Evaluate Reason: It claims “if permanent dipoles are absent, εr varies with temperature.” That reverses the correct logic.Correct logic: absence of permanent dipoles → little T dependence; presence of permanent dipoles → strong T dependence.Therefore, A is true but R is false.

Verification / Alternative check:Classical dielectric theory (Debye model) predicts εr(T) changes for dipolar materials with a 1/T trend, while electronic polarizability changes only slightly with T.

Why Other Options Are Wrong:Any option treating R as correct contradicts the known temperature behavior of dipolar vs non-dipolar dielectrics; declaring A false ignores well-documented material classes.

Common Pitfalls:Confusing ionic with orientational contributions; assuming all dielectrics exhibit strong temperature dependence.

Final Answer:A is true but R is false